This invention relates to a method of controlling the venting of a pressurized fluid to a back pressure chamber.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a pair of scroll members each have a base and a generally spiral wrap extending from the base. The wraps interfit to define compression chambers. One of the two scroll members is driven to orbit relative to the other, and as the two orbit, a fluid entrapped between the wraps is compressed.
Scroll compressors are becoming widely utilized due to several benefits. However, scroll compressors also present design challenges. One main design challenge is the creation of a so-called separating force. As the two scroll members compress the entrapped refrigerant, the trapped refrigerant creates a force trying to separate the two scroll members. This force has an axial component tending to move the two scroll members away from each other. If the two scroll members do move relative to each other, then their wraps will come out of contact with the base of the other scroll member, and a fluid seal will be lost.
To address this separating force scroll compressor designers have tapped a pressurized fluid to a chamber behind one of the two scroll members to resist the separating force. This force, known as a back pressure force, biases the two scroll members together in opposition to the separating force.
Typically, a tap is formed through one of the two scroll members, to tap the compressed refrigerant to the chamber. It is known that the pressure within any one compression chamber will vary during an operational cycle of a scroll compressor between intermediate and higher pressures. As this occurs, the magnitude of the back pressure force varies. The variation in the back pressure force can be seen as a pulsation. The pulsating back pressure force results in unstable operation of the compressor. This problem becomes more acute as the pressure ratios increase.
It has thus been proposed in U.S. Pat. No. 5,762,483 to have a pressure tap which is selectively closed by the wrap of the opposed scroll member such that the scroll compressor designer can select what portions of the operational cycle are tapped into the back pressure chamber. In this fashion, the scroll compressor designer can minimize or even eliminate the pulsations, and have better control over the pressure existing in the back pressure chamber.
It would be desirable to provide other ways of achieving this control over the back pressure.
In the disclosed embodiment of this invention, the tap for tapping a refrigerant from a compression chamber is selectively closed by a portion associated with the housing member such that refrigerant tapping only occurs during selected portions of the orbiting cycle. This device allows the designer to effectively xe2x80x9ccustomizexe2x80x9d the back chamber characteristics by sampling intermediate pressure gas from only selected portions of the compression cycle.
More preferably, the tap is through the orbiting scroll, and the crankcase which supports the orbiting scroll carries a component which selectively opens and closes the tap to communicate with the back pressure chamber. The structure is preferably a valve plate which is biased away from the crankcase and into contact with the rear face of the orbiting scroll. The component has a surface which blocks the tap from communicating with the back pressure chamber during selected portions of the orbiting cycle. More preferably, the plate also has other undercut or recessed portions which will allow refrigerant to move through the tap and into the back pressure chamber.
The component is preferably biased into the base of the orbiting scroll to achieve this control. The bias can be achieved by spring force, magnetic force, or other forces.
In one embodiment, the plate would have a location such that it will block flow over portions of the orbiting cycle, but will not be aligned with the tap during other portions. In this fashion, the tailored control of the fluid being delivered to the back pressure chamber can be easily received.
Preferably, some feature is provided to ensure that the plate is properly positioned relative to the tap. Thus, if the plate is asymmetric, some anti-clocking feature is provided. Alternatively, the plate may be designed to be generally symmetric, such as concentric, and no anti-clocking feature will be necessary.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.